how to explain this arm-pcr result - (Jan/01/2012 )

we are first year student.
hope your help!
thank you so much!

help us please . We dont know why 2 times of running ARM-PCR so different

i answered that because off contaminant, but our instructor didnt agree and want us give more details, more other options.

Do you have a control negative (H2O)? If the band also appear with the control negative, it means your preparation is contaminated by gDNA I think. Let see in the topic " PCR Contamination issues" and verify step by step.
Good luck

we didnt make negative control Thats why we are not sure it has contamination or not ! In the slide of ARM-PCR , we confused why do we have a light bright band underneath the 100bp band in the ladder well dear
Hope to hear from u soon
thanks